1. Field of Invention
Embodiments of the present invention relate generally to methods of forming semiconductor devices, and more particularly to a method of re-oxidizing a gate in a non-volatile memory device.
2. Discussion of the Related Art
Typically, after forming a gate pattern, a re-oxidation process is performed to heal etching damage created within the gate pattern. For example, a selective re-oxidation process is performed on a gate pattern formed of polysilicon and tungsten. The selective re-oxidation process may be performed in an ambient atmosphere containing H2O and H2 in which only an etching damage of the polysilicon is oxidized due to an oxidative difference between tungsten and polysilicon.
However, in a charge trap flash (CTF) structure, a metal nitride layer such as TiN or TaN may be interposed between a tungsten layer and a charge storage layer. Since both TiN and TaN are oxidized in a re-oxidation process, gate characteristics of the charge trap flash (CTF) structure can become deteriorated.
FIG. 1 is a SEM picture illustrating a metal nitride layer that has been oxidized according to a related art re-oxidation process. During a related art re-oxidation process, TiN is oxidized to form TiO2. Because TiN or TaN is oxidized in a re-oxidation process, a bridge can occur in the gate pattern or a threshold voltage scattering characteristic of the gate pattern can become deteriorated.
FIG. 2 is a SEM picture illustrating a surface of a metal nitride layer that has been oxidized according to a related art re-oxidation process. Due to oxidation of TiN, the surface morphology of TiN is very irregular. When the surface morphology of TiN is irregular, characteristics of the gate pattern can become deteriorated, thereby degrading the reliability of a charge trap flash structure incorporating the metal nitride layer as a gate material.